As white LEDs, those of the type in which pseudo-white light is obtained by combining a blue LED chip with a yellow phosphor are widely used. However, while white LEDs of this type fall within the white color range in terms of their chromaticity coordinate values, they have few emitted light components in the red color range and the like, so the appearance of an object illuminated by such a white LED differs considerably from the appearance of an object illuminated with natural light. In other words, such white LEDs have poor color rendering properties which are an indicator of the naturalness of appearance of objects.
Therefore, white LEDs with improved color rendering properties have been developed for practical use by combining red phosphors, orange phosphors or the like in addition to yellow phosphors, so as to compensate for the insufficient red components.
As such red phosphors, nitride phosphors and oxynitride phosphors activated with Eu2+ are known. Representative of these phosphors are Sr2Si5N8:Eu2+, CaAlSiN3:Eu2+, (Ca,Sr)AlSiN3:Eu2+ and the like.
However, phosphors in which Eu2+ is activated as the light emission central ion have a light emission spectrum with a broad half value width, so they have a tendency to include relatively many spectral components in wavelength regions outside the range visible to humans, and they have difficulty in achieving high luminance.
In recent years, phosphors using Eu3+ and Mn4+ as the light emission central ions have been developed as red phosphors having light emission spectra with narrow half value width and including many spectral components in regions of high visual sensitivity. Patent Documents 1 to 4 disclose phosphors in which Mn4+ is activated in complex fluoride crystal K2SiF6, and light emitting devices using these phosphors. These phosphors are capable of achieving red light emissions with a narrow half value width, and the light emitting devices using these phosphors are held to achieve excellent color rendering properties and color reproducibility.